A power supply (PS), in particular a switched mode power supply (SMPS) converts electric energy taken from a primary source of electrical power to electrical energy having parameters different than parameters of energy from the primary source. In particular, a PS intended for welding purposes may deliver electric power of direct current (DC) and alternate current (AC). The latter type of PS is often used for submerged arc welding (SAW) and gas tungsten arc welding (GTAW), better known as tungsten inert gas (TIG) welding. Welding processes conducted with alternating current have many challenges, but due to technological difficulties in welding of certain metals and alloys as well as welding of elements of certain geometrical form and position, AC welding may be an appropriate choice.
There are a number of disadvantages, special requirements and conditions related to AC welding. In AC welding, the polarity of the voltage and direction of the current are periodically changing, such as at a rate of 10 Hz to 1000 Hz, merely as an example. This periodic change means that at certain points in time the current crosses a zero value, resulting in a condition where there is no electric arc and the output circuit is open. During a zero crossing event, the change of voltage polarity precedes the change of current direction. The explanation for this relationship lies in the presence of an inductance in the output circuit. After the change of voltage polarity, first the electric arc or conductive path must be restored. Once conduction is restored, the current rises up, with a rate dependent on voltage capacity and a sum of inductances in the output circuit. In AC power supplies using sinusoidal AC current, the voltage changes in a sinusoidal way at low frequencies. Usually the change is not fast enough to ignite arc plasma particles present in the electric arc, which particles disappear rapidly from the space between weld electrodes. In this circumstance, just a high voltage can ignite arc again. Usually, in an AC welding power supply with sinusoidal output, an ignition unit is used to generate a high voltage surge during every change of the polarity, which circumstance is undesirable for several reasons. In particular, the ignition unit may be a high voltage, high frequency generator, which unit produces copious amounts of electromagnetic interference of very high frequency. An alternative way of arc ignition is to establish voltage of the opposite polarity and increase current of the opposite direction as fast as is possible. Regarding the last requirement, the current at least should undergo direction reversal in a range of current near the zero point, large enough to sustain the electric arc as long as possible, then sustain the arc after ignition with reverse polarity. The limitation of a fast current transition to the initial range arises from a trade-off between process stability and the limitation of the contents of high frequency harmonics of the current. In particular, high frequency harmonics of the welding current invokes effects including: a) high levels of acoustic noise, b) high levels of high frequency magnetic field around the power cables, and c) high frequency losses in the power cables. In any case, a solution for AC current welding is useful if providing rapid changes of the output voltage and the output current.
Another challenge in AC welding is the ignition of an arc after change of polarity. Even under conditions of rapid voltage change, the voltage level may not be sufficient to ignite the arc after polarity change. Therefore, power supplies that can deliver increased voltage are desirable. This feature also addresses the demand for high rate of the current change. Notably, TIG welding power supplies usually contain an inductor, operating temporarily as very high voltage transformer, connected in series, having an inductance more than one order of magnitude larger compared to the inductance of the rest of the circuit. This inductor has very low saturation current, on level of a few amps, but still opposes buildup of the current until saturated, and may accordingly significantly affect ignition of the arc after polarity change.
Another challenge is power supply efficiency. SMPSs deliver energy through a high frequency transformer. The high frequency AC voltage is rectified to DC voltage on the secondary side, where the DC voltage is then converted to low frequency AC voltage by means of a power inverter, which inverter should be capable of delivering alternate current in the entire predicted range. This inverter is an additional link in power conversion, which link decreases efficiency and increases costs.
With respect to these and other considerations, the present disclosure is provided.